Ultra short wave device



ULTRA SHORT WAVE DEVICE Filed July 15, 1958 Fig.1.

- r0 0071 anal/ MR A lhvenbor: i William C. Hahn,

e His Attorney- Patented Feb. 13, 1940 ULTRA SHORT WAVE DEVICE WilliamC. Hahn, Scotia, N. Y., assignor to General Electric Company, acorporation of New York Application July 15, 1938, Serial No. 219,386

6 Claims.

The present invention comprises improvements in ultra short wave devicesof the general type described and claimed in my prior application,Serial No. 153,602 which was filed July 14, 1937,

and of which this application is a continuation in part. This inventionrelates particularly to converters or mixing tubes which can be used atwave lengths on the order of from five meters to five centimeters orless.

As was pointed out in the aforesaid application, an electron stream maybe modulated either as to electron velocity or as to charge density. Thefirst type of modulation involves the production of systematicirregularities in electron velocity from point to point along the beam.The second involves the production of charge density variations, suchvariations being manifested as systematic irregularities in the electrongrouping.

In the conventional design of electronic discharge devices nodistinction is made between these two types of modulation. In connectionwith ultra short-wave devices, however, it is advantageous to utilizeelectrodes which are capable of producing velocity modulation withoutsimultaneously causing appreciable charge density varations. For reasonswhich need not be elabarated here this expedient avoids theobjectionable decrease in input impedance which is observed withconventional prior art devices when they are operated at extremely highfrequencies. Velocity modulation produced as above specified may besubsequently converted into charge density modulation of a higher orderof magnitude to obtain amplification effects.

The foregoing matters are explained in detail in my prior application,Serial No. 153,602. It is an object of the present invention to providemeans whereby the principles described in such application may beapplied to so-called converters or super-heterodyne detectors in whichsignal oscillations are mixed or combined with 10- cally generatedoscillations of fixed frequency to produce other oscillations ofintermediate frequency.

The novel features which I desire to protect herein are pointed out withparticularity in the appended claims. The invention itself, togetherwith further objects and advantages thereof, may best be understood byreference to the following description taken in connection with thedrawing in which Fig. 1 represents a sectional view of a convertersuitably embodying the invention; Fig. 2 shows a modified embodiment;Fig. 3 il- 5 lustrates a further application of the invention inconnection with a device which is adapted to serve both as a converterand a super-regenerative detector, and Fig. 4 is a graphicalrepresentation useful in explaining the invention.

Referring particularly to Fig. 1, there is shown an elongated sealedmetallic envelop l0 closed at one end by means of a base portion II. Theenvelope encloses an electron gun for producing a relativelyconcentrated beam of electrons. In the particular case illustrated, thegun includes a cathode which is constituted of a heater l3 (shown indotted outline) and an emitting cylinder l4 surrounding the heater. Aconducting cylinder I5 surrounds the cathode and when properly biasedwith respect to it, serves to focus the emitted electrons into a beam ofappropriately small dimensions. The cylinder I5 is supported directly byan insulating sleeve 16 and indirectly by a second metallic cylinder H.The latter in turn is supported by being mechanically connected to anapertured barrier l8 which extends transversely across the envelope.

The elements so far referred to are energized by means of lead-inconnections connected with a series of bayonet contacts 20, 2| and 22mounted on the base of the envelope. Through these contacts the cathodeheater I3 is energized by means of a low voltage potential source shownas a battery 24, while the cylinder I5 is maintained at a desiredpotential by means of another potential source 26. A third potentialsource 21, capable of developing from one to sev eralhundred volts,serves to maintain the envelope l0 and especially the barrier l8 at ahigh positive potential with respect to the cathode so as to produceconsiderable acceleration of the electrons emitted by the latter. Ifdesired, magnetic or electrostatic focusing means may be provided inconnection with the device in order to prevent undue spreading of theelectron beam.

In operation, means must be provided for modulating the electron beam soas to produce variations therein corresponding to the variations of areceived signal. Furthermore, as explained in my aforesaid priorapplication, for satisfactory use at high frequencies such variationsshould comprise a maximum of velocity modulation with a minimum ofattendant charge density modulation produced in the vicinity of themodulating electrode structure. This result may be obtained by the useof a modulating space which is sufiiciently shielded from the electrodesource or cathode so that the application of potentials adapted toproduce velocity modulation does not necessarily react on the cathode toproduce corresponding charge density variations. In the particular caseillustrated such a modulating space is provided between the transversebarrier l8 and a similar barrier 30 which is spaced therefrom. Thesebarriers are respectively provided with openings 3| and 32 which permitthe electron beam to pass through the modulating space. They aredirectly maintained at the same potential by being connected directly totheenvelope l0.

Within the modulating space there is provided a control electrode in theform of a hollow tubular conducting member 34 which is adapted to betraversed by the beam. As explained in my aforementioned priorapplication, if the otential level of this electrode is caused to riseand fall cyclically with respect to the boundary potentials of themodulating chamber (that is the potentials of the barriers l8 and 30)longitudinal velocity modulation of the beam is produced. This effect isa maximum when the length of the electrode 34 in the direction of thebeam axis is I such that the electron transit time therethroughcorresponds to a half cycle of the control potential or to an odd numberof such half-cycles. Under these conditions, an electron which entersthe modulating space at a time when the poten-- tial level of theelectrode 34 is maximum is twice accelerated; once as it approaches theelectrode, and again as it leaves the electrode. Similarly, an electronwhich enters the modulating chamber one half-cycle later is twicedecelerated as it traverses the chamber. As a consequence of thesesuccessive accelerations and decelerations the electron beam issuingfrom the modulating space is velocity modulated in the sense of beingcharacterized by successive variations in electron velocity from pointto point along the beam.

The potential applied to the electrode 34 may comprise a modulatedsignal derived, for example, from an antenna 40. This is coupled to theelectrode through a tuned circuit comprising an inductance 4| and acondenser 42. A battery 43 serves to maintain the average potentiallevel of the electrode 34 in a desired relation to that of the barriersl8 and 30. Although such a relationship is not necessary, it isgenerally convenient to have the electrode and the barriers atapproximately the same average potential.

With an arrangement such as that described. the velocity modulation ofthe beam issuing from the aperture 32 will have frequency componentscorresponding to those of the signal impressed on it. For converteroperation, it is necessary additionally tomodulate the beam by means ofa fixed frequency having a desired relationship to the signal frequency.This further modulation may be accomplished in a second modulatingchamber similar to the chamber already described.

The second modulating chamber may be formed, for example, between thetransverse barrier 3D and another barrier 46 which has a central opening41. A tubular electrode 49, generally similar to the electrode 34, isenclosed within this chamber and is excited by connection to anoscillatory circuit comprising an inductance 50 and a variable condenser5|. Assuming this circuit to be maintained in a condition of oscillationat a fixed frequency (by means hereinafter to be described), secondarymodulation ofthe beam is produced. within the chamber so that the beamissuing from the opening 41 has modulation components of the fixedfrequency as well as of the signal frequency; For converter operation,means must mixing these frequencies, preferably under conditions adaptedsimultaneously to produce amplification effects.

This is accomplished in accordance with my present invention by the useof a retarding field for reversing the lower velocity elements of themodulated beam. As explained in my aforemenapplication, Serial No.153.602, this procedure is effective to convert the velocity modulationof the beam into charged density modulation of a higher order ofmagnitude. This is due to the fact that the reversed portion of the beamis constituted of spaced groups of lower velocity electrons, The highervelocity electrons are collected by a collecting anode.

The beam-reversing function isaccomplished inthe present case by anelectrode arranged in the beam path and maintained at a potential notfar from that of the cathode I 4. The relationship between the velocitymodulatiton of the random velocity beam, and may be very high forpractical tube constructions.

For straight amplification purposes it is desirable to operate underchange in charge density modulation. tion, on the other lize someelement ing non-linearly to the electron velocity variations which areproduced in the beam.

Non-linearity is obtained in the present case by so biasing theelectrode 55 as to assure operation at one of the curved portions of thecharhand, itis necessary to uti- To obtain converter or mixer acwhich iscapable of respondsignal and oscillator frequencies but also the sum 5frequencies (i.e., the intermediate frequency) this may be done byproviding in energy-exchanging relation with the reversed component ofthe beam a resonant system which is tuned to such frequency. In thepresent case I employ an oscillatory circuit connectedto the electrode55 and adjusted to oscillate at the intermediate frequency. Thiscircuit, which is shown as'comprisinga condenser 58 and an inductance 59connected in parallel, is excited by the reaction or the reversedcomponent of the electron beam on the electrode. The intermediatefrequency voltage which is thus nal 60 and ground ing tube or to someother utilization device.

be provided for In order to maintain the local oscillator cir- If, asisdeveloped between the term'imay be applied to a succeedcuit 50, 5| insustained oscillation, this also is caused to be affected by thereversed component of the beam. This is done by permitting the returningelectrons to retraverse the electrode 49. In passing through thiselectrode, the charge density variations of the beam will inducecorresponding current variations in the electrode and in its associatedcircuit. Since this circuit is tuned to a fixed frequency and since acomponent of this frequency appears also in the returning beam, there isobviously a tendency for free oscillations of the circuit to occur. Ifthe length of the beam path from electrode 49 to electrode 55 and returnis properly correlated with the beam velocity, these oscillations areselfsustaining. That is to say, the charge density variations of thereturning beam, it correctly phased, produce voltage swings of the grideffective to maintain the system in continuous oscillation. Thiscondition may be obtained for a particular case by properly adjustingthe tube dimensions and the beam velocity.

It is not desired that the returning beam shall reenter the firstmodulating chamber, since to permit it to do so would result in anobjectionable reaction on the electrode 34 and the associated inputcircuit. This may be avoided by tilting the electrode 55 to cause thereversed component of the beam to travel at an angle to the main beampath as indicated by the dotted line a. By this means the beam is causedto impinge on the solid portion of the barrier 30 and to be collectedthereby. (The feature of a tilted electrode used as a beam reversingmeans is the prior invention of Harry C. Thorson and is fully describedand claimed by him in his application S. N. 264,877, filed March 30,1939, and assigned to the same assignee as the present application.)

In Fig. 2 I have shown an alternative embodiment of the invention. Inthis arrangement the elements of the electron gun and of the firstmodulating chamber are similar to those described in connection withFig. l and are, therefore, similarly numbered. The modulated beamissuing from the opening 32 traverses a series of further chambersformed by a succession of transverse barriers 65, 66 and 61. Thesechambers respectively enclose electrodes 69, 10 and H, of which the lastis connected to a local oscillator circuit comprising a condenser 12 andan inductance 13.

After traversing the oscillator electrode H the beam approaches anelectrode 14 which is so biased by means of a battery 15 as to returnthe lower velocity components of the beam. In accordance with theprinciples already described, the operation of this electrode is toproduce mixer action.

The reversed portion of the beam, containing components corresponding tothe signal and oscillator frequencies as well as to their sum anddifference, is caused to traverse both the chamber bounded by thebarriers 61 and 66 and that bounded by barriers 66 and 65. In the formerof these it acts to excite the electrode H so as to maintain theassociated tuned circuit in a state of oscillation. In the latter ittraverses the electrode 10 which is connected to a condenser 11 and aninductance 18, these constituting an intermediate frequency tankcircuit. Output terminals 19 for the intermediate frequency circuit areprovided in connection with an inductance which is coupled to the tankinductance 18. After its passage through the electrode 10 the reversedcomponent of the beam is collected by being allowed to impinge on thebarrier 65.

The charge density variations of the reversed portion of the beam tendto produce corresponding current variations in the electrode 10 and inits associated circuit. Due to its tuning, the latter is selectivelyresponsive to stimulation by the intermediate frequency component ofthese variations and, therefore, oscillates at such frequency.

For best operation, the impedance of the intermediate frequency circuitshould be high, which condition is attained only if the reaction of thecircuit on the beam is relatively slight. In order to assure this resultmeans are provided to minimize the tendency of the electrode 10 tovelocity modulate the main beam-as it normally tends to do. In thepresent instance, this is accomplished by the provision of acomplementary or neutralizing electrode 69 which is directly connectedto the electrode 10. With this arrangement, potential variations of theelectrode Ill are communicated directly to electrode 69 and cause acorresponding variation of its potential. If the length of each of theseelectrodes in the direction of the beam axis is such that the electrontransit time through each corresponds approximately to a half cycle ofthe intermediate frequency, the modulating effect of the electrode 10 isoffset by the equal and opposite effect produced by the electrode 69.That is to say, a given electron, which is to be accelerated a givenamount by the electrode 10, is decelerated a precisely equal amount bythe electrode 69. Consequently, any electron which traverses bothelectrodes experiences no net change in velocity. As a result, theimpedance of both electrodes is high as far as their reaction on thebeam is concerned.

The modification shown in Fig. 3 comprises an arrangement by whichfrequency mixing and super-regenerative detection can be accomplished ina single device. In this figure, elements which have been previouslydescribed in connection with Figs. 1 and 2 bear the same numerals inFig. 3.

In the use of the combination shown, the signal modulated beam issuingfrom opening 32 is additionally modulated by means of an electrode 80which is coupled to a local oscillator (not shown) through a tunedcircuit comprising an inductance 82 and a condenser 83. Thereafter thebeam is caused to traverse another modulate ing chamber which is boundedby transverse diaphragms 85 and 86 and which contains a tubularelectrode 81. After leaving this chamber the lower velocity componentsof the beam are returned to it by the action of a retarding fieldprovided by an electrode 89.

In accordance with the principlesexplained in connection with theoscillator electrode 49 of Fig. 1, the reaction of the returningcomponent of the beam on the electrode 81 is such as to maintain thetuned circuit with which it is connected in continuous oscillation. Thiscircuit, which comprises a condenser 9| and an inductance 92, is tunedto the intermediate frequency which corresponds to the differencebetween the signal frequency and the frequency developed by the localoscillator. In operation, it reacts on the-portion of the beamproceeding toward the electrode 89 to increase the velocity modulationthereof. (Since the electrode 8'! is not in this case used as an outputelectrode, the considerations mentioned in connection with Fig. 2concerning the need for limiting the reaction of the electrode H! on thebeam do not apply.)

In order to obtain super-regenerative operation, means are provided forintermittently interrupting the Oscillations of the intermediatefrequency circuit. Such intermittent interruption may be accomplished byapplying either to the'electrode 89 or to some other part of the system,quench oscillations having a super-audible frequency appreciably lowerthan the intermediate frequency. The quench is provided in the presentcase by means of a tuned circuit comprising a condenser 94 and aninductance 95, the latter being coupled to a source of quenchoscillations (not shown). I

As a result of the arrangement specified, intermittent oscillations ofthe intermediate frequency circuit will occur, the instantaneousmagnitude of such oscillations being a functionof the magnitude of theintermediate frequency component of the returning beam. Since thislatter quantity is in turn proportional to the 0 modulation or audiocomponent of thesignal applied to theelectrode 34, it is apparent thatsuper-regenerative operation may be obtained. The amplified audio ormodulation component may be selectively detected by the provision of alow frequency circuit connected to electrode 89, or to a separateelectrode coupled with some portion of the beam in which it appears. Inthe present case such a circuit is provided by a signal translatingdevice (shown diagrammatically as a head phone set 98) connected inseries with a choke coil 99. This latter element serves to prevent thequench oscillations from passing through the head phone set. A blockingcondenser I00 the quench circuit. I

The device described in the foregoing combines the advantages of highsensitivity and high amplification. It is, furthermore, characterized ba high degree of noise suppression.

0 While I have described my invention in con- P u e velocity variationsin the electron ts, connected with one *such electrode to produceelectron velocity variations in the stream corresponding to a signalfrenection with particular embodiments thereof, it will beunderstoodthat various modifications may be made-by those skilled in the artwithout departing from theinvention. I, therefore, aim in the appendedclaims to cover .of structure and use as fall within the true spirit ofthe foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A converter'comprising means including a cathode for developing anelectron stream, a pair of successively arranged electrodes operable tostream, said electrodes being sufiiciently shielded from the cathode so.as to be incapable at normally applied potentials of producingappreciable chargedensity variations in the stream, means of saidelectrodes for causing quency, means connected with the other electrodefor causing such electrode to produce electron velocity variations inthe stream at a fixed frequency different from the signal frequency,means reacting on the stream in a manner which varies non-linearly withthe velocity of the stream, thereby to obtain in the stream chargedensity variations having frequency components resulting from the mixingof the said signal and fixed frequencies, and means selectivelyresponsive to a particular frequency resulting from such mixing forabstracting energy from the stream.

2. In combination, means including an electron gun for producing aconcentrated beam of electrons, a series of electrodes electrostaticallyof a potential having excludes the audio frequency from all suchvariations a partlcularirequency resulting from such mixing forabstracting energy from the beam.

3. A converter including means for developing an electron beam, meansfor producing velocity modulation of the beam by means of a potential ofsignal frequency, means for producing additional velocity modulation ofthe beam by means a selected frequency different from the signalfrequency, means providing reversing at least a portion to thedifference between the signal frequency and the selected frequency,

the beam at a fixed frequency'other than signal frequency, meansreacting on the doubly modulated beam to produce mixing of the signaland fixed frequencies, an oscillatory circuit which is resonant at anintermediate frequency produced by such mixing, coupling means causingsaid cirtionof intermediate frequency oscillations in the said circuit,and signal translating means coupled to the beam afterits reaction withthe circuit, said last-named means being selectively responsive to themodulation component of the signal.

6. In combination, means comprising an electron gun for producing arelatively concentrated beam of electrons, a series of electrodesarranged along the beam path and adapted to influence the beamsuccessively, means connecting with one of said electrodes for producingvariations in electron velocity at a frequency corresponding to that ofa modulated signal, means connecting with another of said electrodes forproducing additional electron velocity variations at a fixed frequencydifferent from the signal frequency, means acting on the beam after itstraversal of the said electrodes and effective to reverse at least thelower velocity components of the beam, thereby to produce mixing of thesaid signal and fixed frequencies, an oscillatory circuit which is tunedto an intermediate frequency produced by such mixing, said circuit beingconnected to one of said electrodes which is traversed both by the mainbeam and by the reversed components thereof, means including a source ofquench oscillations for periodically terminating the oscillationsproduced in the said circuit by the reaction thereon of the reversedcomponent of the beam, and signal translating means selectivelyresponsive to the modulation component of the signal, said last-namedmeans being in energy-exchanging relation with a portion of the beamaffected by the intermediate frequency oscillations produced in the saidcircuit.

WILLIAM C. HAHN.

